In general, it is widely known to use polyurethane resins excellent in flexibility at ordinary temperature, adhesion property and chemical resistance as sealing materials for hollow-fiber membrane modules (hollow-fiber membrane type filter devices) constituting blood processors, water purifiers or industrial water treatment apparatus.
In recent years, based on a background of a demand for more improvement in throughput capacity, there is a tendency that the hollow-fiber membrane module is enlarged day by day particularly in industrial water treatment apparatus. Therefore, it has also been required that a sealing material used can meet the demand for the enlargement of the hollow-fiber membrane module.
As a composition for obtaining a sealing material for a membrane module constituting a blood processor or water purifier, there has heretofore been proposed a polyurethane resin forming composition using an amine type polyol as a component of a curing agent (see, for example, Patent Document 1).
However, the polyurethane resin forming composition cannot be applied to production of a large-sized hollow-fiber membrane module because curing rate is too high. Therefore, the composition is insufficient to be put to practical use particularly in industrial water treatment apparatus.
As a composition for obtaining a sealing material for membrane modules constituting a blood processor or water purifier, there has also been proposed a polyurethane resin forming composition making combined use of an amine type polyol and a polyoxyalkylene compound having a specific active hydrogen-containing group as components of a curing agent (see, for example, Patent Document 2).
However, a sealing material obtained from the polyurethane resin forming composition is poor in heat resistance and large in the amount of substance eluted into water when immersed in the water. Therefore, the composition is insufficient to be put to practical use particularly in industrial water treatment apparatus.
Moreover, as a composition for obtaining a sealing material for a hollow-fiber membrane module, there has been proposed a polyurethane resin forming composition using a polyether polyol having a nominal functional group number of 6 or more as a component of a curing agent (see, for example, Patent Document 3).
However, a sealing material obtained from the polyurethane resin forming composition is large in the amount of substance eluted into water when immersed in the water. Therefore, the composition is insufficient to be put to practical use particularly in industrial water treatment apparatus.
Furthermore, as a composition for obtaining a sealing material for membrane modules, there has been proposed a polyurethane resin forming composition using a prepolymer obtained from an excess amount of an organic polyisocyanate and an alkylene (having 2 to 5 carbon atoms) glycol having at least one methyl group at a side chain as a component of a main agent (see, for example, Patent Document 4).
However, a sealing material obtained from the polyurethane resin forming composition is poor in heat resistance. Therefore, the composition is insufficient to be put to practical use particularly in industrial water treatment apparatus.
In addition, as a polyurethane resin forming composition for a membrane sealing material, there has been proposed a composition composed of an isocyanate component (a main agent) and a polyol component (a curing agent) and using a caster oil-modified polyol obtained from castor oil and/or a castor oil fatty acid and a trimethylolalkane as a polyol component (see, for example, Patent Document 5).
However, a sealing material obtained from the polyurethane resin forming composition shows a high temperature dependency of hardness and thus does not result in a sufficient hardness under a high-temperature environment. Therefore, further improvement is desired particularly in industrial water treatment apparatus.
As described above, all the sealing materials obtained from the conventionally known polyurethane resin forming compositions are insufficient to be put to practical use in industrial water treatment apparatus constituted by large-sized hollow-fiber membrane modules, and there is thus a strong demand for providing a sealing material (a polyurethane resin forming composition for obtaining such a sealing material) capable of being put to practical use in such applications.    Patent Document 1: JP-A-6-100649 (pp. 2-4)    Patent Document 2: JP-A-2000-128952 (pp. 2-4)    Patent Document 3: JP-A-2002-128858 (pp. 2-5)    Patent Document 4: JP-A-9-48835 (pp. 2-4)    Patent Document 5: JP-A-2005-89491